The case is being closely watched because it could establish new constitutional benchmarks in advance of the approaching 2008 general elections. If the high court upholds the Indiana law, the action would give a green light to the kinds of aggressive efforts to fight voter fraud favored by many Republicans. If instead the court invalidates the Indiana law, it would signal a heightened duty to keep it as easy as possible for all citizens to exercise their right to vote.

"This case is going to have serious ramifications not only for photo-ID laws but for what the right to vote means, and to what extent state and local governments have the ability to infringe that right," says Jon Greenbaum, director of the Voting Rights Project at the Lawyers' Committee for Civil Rights Under Law.

Other analysts say the Indiana voter-ID case is being blown out of proportion.

"There may be much less at stake in this case than meets the eye," Bradley Smith, former chairman of the Federal Election Commission, said in a recent press briefing. "For all the excitement it has generated, the fact is there is very little evidence that there is a lot of voter fraud that these [ID] laws will prevent, and there is very little evidence that people aren't able to vote because of these laws."

Mr. Smith says the Supreme Court should have waited for a better case. Others disagree.

"Indiana has enacted the most stringent and restrictive voter identification requirement in the United States," writes Kenneth Falk, a lawyer with the American Civil Liberties Union of Indiana, in his brief to the court. "The severe burden imposed by the statute is not, and cannot be, justified."

While the vast majority of Indiana voters possess either a driver's license or some other form of photo ID, an estimated 43,000 Indiana residents do not. The state will issue a photo identification card free of charge to anyone who requests it, but critics say assembling the three documents necessary to get the free ID card can cost significant time and money.

The burden of the law falls primarily on elderly, disabled, poor, and minority voters. Those who fall within such classifications generally vote for Democrats, critics of the law say.

Two Democratic officials, the Indiana Democratic Party, and four public interest groups challenged the law in US district court. A federal judge ruled the law was constitutional. The ruling was upheld 2 to 1 by the Seventh US Circuit Court of Appeals in Chicago. The Supreme Court agreed in September to hear the appeal.

The law was passed in recognition that Indiana is increasingly vulnerable to in-person election fraud, according to Indiana Solicitor General Thomas Fisher. It was not enacted to undercut Democratic voters and candidates, he says.

In his brief to the court, Mr. Fisher says those who sued to overturn the law lack legal standing to bring such a suit because none of them has been harmed by the law. There is no evidence, he adds, any individual has ever been prevented from voting because of the photo ID law.

"How onerous can the law be if a major political party, two seasoned candidates, and four substantial political interest groups cannot find even one person injured by it?" Fisher writes.

Opponents of the law counter that no one has ever been prosecuted for in-person voter fraud in Indiana, and there have been no reports of anyone posing as someone else while trying to vote in an Indiana election.

"What the legislators who passed the Photo ID Law did know was that it would burden voting by a group of eligible voters who lack the requisite identification because they do not drive and have no other regular need for state-issued photo ID," writes Washington lawyer Paul Smith, in his brief on behalf of the Indiana Democratic Party.

Mr. Smith says the law will discourage or deter low-income, minority, disabled, and senior-citizen voters from going to the polls. "Because these voters tend to support Democratic candidates, there was good reason to think that the suppression of turnout caused by the new law would primarily harm Democrats," Smith writes.

"The law was passed by a party-line vote shortly after the Republican Party won control of both houses of the state legislature as well as the governor's office," Smith writes.

Lawyers for Indiana say the opponents' case is based on speculation. A published study of Indiana voter turnout since the photo ID law took effect shows that voter turnout increased statewide by about 2 percent. They say the study did not find any reduction in voter turnout in counties with higher percentages of minority, poor, elderly, or less educated residents.

Opponents of the law say that the offer of a free ID card does not necessarily reduce the burden on certain potential voters. For those who do not drive, merely getting to the state ID office involves an investment in time and logistics. In addition, gathering the necessary paperwork can be problematic.

They cite the case of Theresa Clemente, who moved from Massachusetts to Indiana in 1991. Earlier in the case, she testified that she made three unsuccessful trips to the state motor-vehicles bureau to obtain a free photo ID card.

Ms. Clemente arrived with her Social Security card, her voter-registration card, her property tax bill, a utility bill, and a credit card. She was told she must produce a copy of her birth certificate.

But when she returned with the document, she was told she needed a certified copy of the birth certificate.

The certified birth certificate cost $28 and was mailed to her 14 days later. When she returned to the motor-vehicles bureau, she was told that because her birth certificate used only her maiden name she must also provide a certified copy of her marriage license.

"For many affluent Americans it may be hard to imagine life without a driver's license, a passport, or other government-issued photo ID," writes Smith in his brief. "The reality is that, across the country, about 12 percent of voting-age Americans lack a driver's license," he writes.